WO2023181443A1

WO2023181443A1 - Thermal insulation material

Info

Publication number: WO2023181443A1
Application number: PCT/JP2022/029291
Authority: WO
Inventors: 祐太朗田口; 成輝神田
Original assignee: 住友理工株式会社
Priority date: 2022-03-25
Filing date: 2022-07-29
Publication date: 2023-09-28
Also published as: US20240025813A1; JPWO2023181443A1

Abstract

This thermal insulation material is provided with a thermal insulation layer which has: a porous structure for forming a skeleton where a plurality of particles are connected while having pores inside and having a hydrophobic site on the surface thereof or on the surface and on the inside; infrared ray-shielding particles; and inorganic fibers. Said thermal insulation layer satisfies the following conditions (a)-(d). The content of the components in conditions (a)-(d) are calculated based on the mass of the thermal insulation layer overall being 100 mass%. (a) The content of said inorganic fibers is 5-25 mass%, inclusive. (b) The content of said infrared ray-shielding particles is 10 mass% or higher. (c) The content obtained by combining the porous structure and the infrared ray-shielding particles is 70 mass% or higher. (d) The ratio of the content of the porous structure to the content of the infrared ray-shielding particles is 1.2 or higher.

Description

insulation material

The present disclosure relates to a heat insulating material using a porous structure such as silica airgel.

A variety of insulation materials have been used for the purpose of controlling heat flow in automotive parts, housing materials, industrial equipment, etc. Silica airgel, which has low thermal conductivity, is known as a material for heat insulating materials. For example, in a battery pack installed in a hybrid vehicle, an electric vehicle, etc., a heat insulating material is placed between adjacent battery cells. This type of heat insulating material is required to have high heat insulating properties, especially at high temperatures, so that it can suppress heat transfer and suppress thermal runaway when a battery cell generates abnormal heat.

For example, Patent Document 1 describes a composite heat insulating material in which a heat insulating layer containing silica airgel, short silica fibers, and an infrared absorbing material is sandwiched between two base fabrics. Paragraph [0048] of the same document states that the infrared absorbing material is an effective heat retaining material when it is desired to maintain a high temperature range of 400 to 900°C. Patent Document 2 describes a heat insulating material having an airgel fiber body in which a fiber base material is filled with silica airgel, and a porous coating layer covering the airgel fiber body. Paragraphs [0052] and [0056] of the same document state that when an infrared reflector or an infrared absorber is added to the airgel fiber body (insulating layer), radiant heat from the heat source can be effectively blocked. Patent Document 3 describes a heat insulating material that includes silica airgel, ceramic crystals, inorganic fibers, and an infrared-active material. Paragraph [0041] of the same document states that silicon carbide and titanium oxide are effective in reducing radiant heat energy. Patent Document 4 describes a heat insulating material made by mixing silica airgel powder with an average particle diameter of 0.01 mm to 4.0 mm and silicon carbide powder with an average particle diameter of 2 μm. Paragraph [0016] of the same document states that if the mass ratio of silicon carbide powder is greater than 0 and smaller than 110 to 100 of silica airgel powder, the thermal conductivity can be reduced.

International Publication No. 2021/095279 JP2009-299893A International Publication No. 2013/141189 JP2020-16326A

In silica airgel, a plurality of fine silica particles are connected to form a skeleton, and between the skeletons there are pores smaller than the mean free path of air. This fine porous structure mainly suppresses convection among the three forms of heat transfer (conduction, convection, and radiation), and exhibits high heat insulation properties. Here, radiation is a phenomenon in which heat is transferred by electromagnetic waves, and the higher the temperature, the greater the radiant energy released. Therefore, in a high-temperature atmosphere, radiation becomes the main cause of heat transfer. Therefore, at high temperatures, it is difficult to obtain the desired heat insulation properties with silica airgel alone, and it is effective to incorporate infrared shielding particles as described in Patent Documents 1 to 4 mentioned above.

However, when infrared shielding particles are blended, there is a risk that a heat transfer path may be formed due to the infrared shielding particles connecting with each other. Furthermore, when other materials such as inorganic fibers are blended, these and the infrared shielding particles are connected to each other, thereby making it easier to form a heat transfer path. As a result, heat transfer due to conduction increases, and there is a risk that the heat insulation properties will decrease. Therefore, simply blending infrared shielding particles cannot sufficiently exhibit the effect of suppressing heat transfer at high temperatures. In this regard, Patent Document 4 describes the thermal conductivity of a mixture of silica airgel powder with a predetermined particle diameter and silicon carbide powder mixed at a predetermined ratio. However, in this document, the thermal conductivity was only measured by changing the blending ratio after limiting the particle size of both powders, and the study did not include the filling state of the particles and the formation of heat transfer paths. No consideration has been given to the case of incorporating inorganic fibers, etc.

The present disclosure has been made in view of these circumstances, and an object of the present disclosure is to provide a heat insulating material that uses a porous structure such as silica airgel and has high heat insulation properties even at high temperatures.

In order to solve the above problems, the heat insulating material of the present disclosure includes a porous structure in which a plurality of particles are connected to form a skeleton, have pores inside, and have a hydrophobic site at least on the surface and inside. , infrared shielding particles, and inorganic fibers, and is characterized by a heat insulating layer that satisfies the following conditions (a) to (d). The content of each component under the conditions (a) to (d) is calculated based on the total mass of the heat insulating layer as 100% by mass.
(a) The content of the inorganic fiber is 5% by mass or more and 25% by mass or less.
(b) The content of the infrared shielding particles is 10% by mass or more.
(c) The combined content of the porous structure and the infrared shielding particles is 70% by mass or more.
(d) The ratio of the content of the porous structure to the content of the infrared shielding particles is 1.2 or more.

According to the heat insulating material of the present disclosure, by specifying the blending amounts of the porous structure, infrared shielding particles, and inorganic fibers in the heat insulating layer as shown in (a) to (d), heat transfer due to radiation can be suppressed; By simultaneously suppressing the formation of heat transfer paths, high heat insulation properties can be achieved not only at room temperature but also at high temperatures.

Specifically, by satisfying the condition (a), the formation of heat transfer paths is suppressed while the reinforcing effect of the inorganic fibers is exhibited. By satisfying the condition (b), the transfer of heat due to radiation can be effectively suppressed, and the heat insulation properties at high temperatures are improved. By satisfying the condition (c), the content of the porous structure and the infrared shielding particles that contribute to improving the heat insulation properties is increased, and the heat insulation properties are improved. In addition, since the content of components that make a small contribution to improving heat insulation properties is relatively reduced, the formation of heat transfer paths by these components is suppressed, thereby improving heat insulation properties. By satisfying the condition (d), the porous structure can inhibit the connection between the infrared shielding particles. This makes it difficult to form a heat transfer path and improves heat insulation.

FIG. 2 is a schematic diagram for explaining a method for measuring the reference number of porous structures.

Hereinafter, the heat insulating material of the present disclosure will be described in detail. The heat insulating material of the present disclosure is not limited to the following forms, and can be implemented in various forms with changes and improvements that can be made by those skilled in the art without departing from the gist of the present disclosure. .

<Insulating layer>
The heat insulating material of the present disclosure includes a heat insulating layer that includes a porous structure, infrared shielding particles, and inorganic fibers and satisfies the conditions (a) to (d) described above.

[Porous structure]
A porous structure has a skeleton formed by connecting a plurality of particles and has pores inside. It is desirable that the diameter of the particles forming the skeletons (primary particles) be about 2 to 5 nm, and the size of the pores formed between the skeletons be about 10 to 50 nm. Many of the pores are so-called mesopores with a diameter of 50 nm or less. Since mesopores are smaller than the mean free path of air, air convection is restricted and heat transfer is inhibited. The shape of the porous structure is not particularly limited, such as a spherical shape or an irregularly shaped block, but a chamfered shape or a spherical shape is desirable. In this case, since the dispersibility in the liquid is improved, it becomes easier to prepare a composition for producing a heat insulating layer (composition for a heat insulating layer). In addition, the voids between the porous structures can be reduced to increase the amount of filling, thereby suppressing the connection of the infrared shielding particles, so that the heat insulation properties can be improved. The porous structure may be used in its manufactured state, or may be further pulverized before use. For the pulverization process, a pulverizer such as a jet mill or a spheroidizing apparatus may be used. The pulverization process removes the corners of the particles and gives them a rounded shape. This makes the surface of the heat insulating layer smooth and makes it difficult to crack.

The average particle diameter of the porous structure is preferably about 1 to 200 μm. The larger the particle size of the porous structure, the smaller the surface area and the larger the pore volume, and therefore the greater the effect of improving heat insulation. However, since the infrared shielding particles fill the gaps between the porous structures, if the particle size of the porous structure is large, the area where the infrared shielding particles are not present may become large. . In this case, the frequency with which infrared rays emitted from the heat source impinge on the infrared shielding particles decreases, which may reduce the infrared shielding effect. For example, the average particle diameter of the porous structure is preferably 10 μm or more and 50 μm or more, and when considering the stability of the heat insulating layer composition and the ease of coating, it is preferably 100 μm or less. As the average particle diameter, a median diameter (D ₅₀ ) determined from a volume-based particle size distribution measured by a laser diffraction/scattering method may be adopted. Note that catalog values may be used for commercially available products.

When the particle diameters of the porous structures are different, the small-diameter porous structures fit into the gaps between the large-diameter porous structures. Thereby, the amount of filling can be increased, and the small-diameter porous structure can inhibit the connection of the infrared-shielding particles, so that the effect of improving heat insulation properties is further increased. From this point of view, it is desirable to use a porous structure with a wide particle size distribution, or to use two or more types with different average particle sizes in combination. Further, during the manufacturing process of the heat insulating layer, the stirring conditions of the material may be adjusted so that some of the large diameter particles are pulverized into small diameter particles.

The content of the porous structure may be appropriately determined so as to satisfy the conditions (c) and (d) described above, taking into account the content of infrared shielding particles that also contribute to improving heat insulation properties. For example, the content of the porous structure alone is desirably 40% by mass or more, and more preferably 50% by mass or more, based on the mass of the entire heat insulating layer as 100% by mass. On the other hand, if the number of porous structures increases, the porous structures may easily fall off. Therefore, the content of the porous structure alone is desirably 75% by mass or less, and more preferably 70% by mass or less, based on the mass of the entire heat insulating layer as 100% by mass.

From the viewpoint of realizing a suitable filling state of porous structures in the heat insulating layer, for example, the reference number of porous structures calculated by the following steps (i) to (iii) is 10 or more, and It is desirable that there are 15 or more.
(i) A cross section in the thickness direction of the heat insulating layer is photographed using a scanning electron microscope (SEM) at a magnification of 200 times, and five straight lines each having a length of 400 μm are drawn in parallel at 40 μm intervals on the obtained cross-sectional photograph.
(ii) For each straight line drawn, count the number of porous structures that intersect with the straight line, and calculate the total sum.
(iii) Divide the calculated total by 5 to obtain the reference number of porous structures.

FIG. 1 shows a schematic diagram for explaining the method for measuring the reference number of porous structures. FIG. 1 does not limit the heat insulating layer in any way, including the size, shape, and filling state of the porous structure. As shown in FIG. 1, a porous structure 11, infrared shielding particles 12, and inorganic fibers 13 are observed in a cross-sectional photograph 10 taken by SEM at a magnification of 200 times of a cross section of the heat insulating layer in the thickness direction. The procedure for measuring the reference number of porous structures 11 is as follows. First, five straight lines α, β, γ, δ, and ε are drawn on the cross-sectional photograph 10. The lengths of the five straight lines α, β, γ, δ, and ε are all 400 μm, and the interval between the straight lines is 40 μm. Next, for each of the five straight lines α, β, γ, δ, and ε, the number of porous structures 11 that intersect with the straight line is counted, and the total sum is calculated. Then, the reference number is obtained by dividing the calculated sum by 5. For example, the number of porous structures 11 that intersect with the drawn straight line is v for the straight line α, w for the straight line β, x for the straight line γ, y for the straight line δ, and z for the straight line ε. In this case, the reference number is "(v+w+x+y+z)/5". The reference number is an index that indicates the filling state of the porous structures in the heat insulation layer, and if it is 10 or more, the particle size of the porous structures is not too large and the particles are filled in the gaps between the large-diameter porous structures. It can be determined that a state in which small-diameter porous structures, infrared shielding particles, etc. are appropriately filled has been achieved.

The porous structure has a hydrophobic site at least on the surface and inside. When the surface has a hydrophobic site, it is possible to suppress moisture from seeping into the pores, so the porous structure is maintained and the heat insulation properties are less likely to be impaired. For example, functions such as hydrophobicity can be imparted to the surface of the porous structure by surface treatment with a silane coupling agent or the like. Further, in the manufacturing process of the porous structure, a hydrophobic treatment such as adding a hydrophobic group may be performed.

The type of porous structure is not particularly limited. Examples of primary particles include silica, alumina, zirconia, and titania. Among these, silica airgel in which the primary particles are silica, that is, a plurality of silica fine particles are linked to form a skeleton, is desirable because of its excellent chemical stability. Further, a cohesive structure in which a plurality of fumed silica fine particles are connected to form a skeleton is also suitable.

The method for producing silica airgel is not particularly limited, and the drying step may be performed at normal pressure or supercritical. For example, if the hydrophobization treatment is performed before the drying step, there is no need for supercritical drying, that is, drying can be performed at normal pressure, making it easier and cheaper to manufacture. Due to the difference in drying methods used to produce airgel, those dried under normal pressure are sometimes called "xerogel" and those dried under supercritical conditions are called "aerogel"; however, in this specification, both are referred to as "xerogel". Together, they are referred to as "aerogel."

[Infrared shielding particles]
The infrared shielding particles absorb heat from the heat source and re-emit it from the surface on the heat source side, thereby blocking radiant heat from the heat source and contributing to improved heat insulation, particularly at high temperatures. The particle size of the infrared shielding particles is relatively small from the viewpoint of filling the gaps between the porous structures and suppressing the connection between the infrared shielding particles and other components, making it difficult to form heat transfer paths. is desirable. On the other hand, if the particle size is too small, it becomes difficult for infrared rays to hit the particles, and furthermore, infrared rays are not scattered sufficiently, making it difficult to exhibit the effect of blocking radiant heat. From this point of view, the average particle diameter of the infrared shielding particles is preferably 0.3 μm or more and 22 μm or less. As for the average particle diameter of the infrared shielding particles, the median diameter (D ₅₀ ) determined from the volume-based particle size distribution measured by laser diffraction/scattering method may be adopted, as in the case of the porous structure. Catalog values may be used for products.

Infrared shielding particles include silicon carbide, kaolinite, montmorillonite, silicon nitride, mica, alumina, zirconia, aluminum nitride, titanium oxide, zirconium silicate, zinc oxide, tantalum oxide, tungsten oxide, niobium oxide, indium tin oxide, and Examples include cerium, boron carbide, manganese oxide, tin oxide, bismuth oxide, iron oxide, magnesium oxide, barium titanate, and the like. In particular, from the viewpoint of enhancing the effect of blocking radiant heat, it is desirable that the infrared shielding particles have high emissivity particles having an emissivity of 0.6 or more in the infrared wavelength region. Examples of high emissivity particles include silicon carbide, kaolinite, silicon nitride, mica, alumina, zirconia, aluminum nitride, zirconium silicate, cerium oxide, boron carbide, manganese oxide, tin oxide, iron oxide, and the like. Furthermore, from the viewpoint of scattering incident infrared rays and enhancing the effect of blocking radiant heat, a form having particles having a high refractive index in the infrared wavelength region is also effective. For example, high refractive index particles having a refractive index of 2.0 or more in the visible light wavelength region are suitable. High refractive index particles include silicon carbide, titanium oxide, zirconia, silicon nitride, aluminum nitride, zinc oxide, tantalum oxide, tungsten oxide, niobium oxide, cerium oxide, manganese oxide, tin oxide, bismuth oxide, iron oxide, titanate. Examples include barium.

For example, silicon carbide, titanium oxide, silicon nitride, mica, alumina, aluminum nitride, boron carbide, iron oxide, magnesium oxide, etc. have a relatively large specific heat, so they have a large heat capacity and the particles themselves are difficult to heat. In this respect as well, it contributes to improving the heat insulating properties of the heat insulating layer. In addition, since it has high heat resistance, it also contributes to improving the heat resistance of the heat insulating layer. In particular, silicon carbide is suitable because its thermal conductivity does not increase much even in a high temperature atmosphere of about 800°C.

The content of the infrared shielding particles is 10% by mass or more when the total mass of the heat insulating layer is 100% by mass (condition (b) described above). From the viewpoint of increasing the effect of suppressing heat transfer due to radiation and further improving the heat insulation properties at high temperatures, the content of the infrared shielding particles is preferably 15% by mass or more, more preferably 20% by mass or more. Further, the combined content of the porous structure and the infrared shielding particles is 70% by mass or more when the total mass of the heat insulating layer is 100% by mass (condition (c) described above). From the viewpoint of further improving the heat insulation properties, the total content of the porous structure and the infrared shielding particles is preferably 75% by mass or more, more preferably 80% by mass or more. Further, the ratio of the content of the porous structure to the content of the infrared shielding particles [content of the porous structure (mass%)/content of the infrared shielding particles (mass%)] is 1.2 or more. (Condition (d) above). By blending the porous structure with a mass ratio of 1.2 times or more to the infrared shielding particles, the porous structure inhibits the connection between the infrared shielding particles and suppresses the formation of heat transfer paths. Can be done. In addition, from the viewpoint of increasing the content of the infrared shielding particles to increase the effect of suppressing heat transfer due to radiation, the ratio of the content of the porous structure to the content of the infrared shielding particles is 8 or less. and is suitable.

[Inorganic fiber]
The inorganic fibers are present in a physically entangled manner around the porous structure, thereby improving the mechanical strength of the heat insulating layer and suppressing the porous structure from falling off. The type of inorganic fiber is not particularly limited, but in consideration of heat resistance, mechanical strength, etc., ceramic fibers such as glass fiber and alumina fiber are suitable. The content of the inorganic fibers is 5% by mass or more and 25% by mass or less when the total mass of the heat insulating layer is 100% by mass (the above-mentioned condition (a)). By setting the content of the inorganic fibers within this range, the reinforcing effect of the inorganic fibers can be exhibited while preventing the formation of excessive heat transfer paths. The length of the inorganic fibers is desirably 16 mm or less, considering both the reinforcing effect and the suppression of formation of heat transfer paths.

[Other ingredients]
In addition to the porous structure, infrared shielding particles, and inorganic fibers, the heat insulating layer may also contain other components such as organic additives and reinforcing particles. By the way, from the perspective of ensuring the independence of the insulation layer, that is, making it possible for the insulation layer to support its own weight and be handled on its own, components such as porous structures are bound together. Examples include forms containing a binder. However, if a binder is present on the surface or in the gaps of a component such as a porous structure, there is a risk that a heat transfer path will be formed through the binder. Therefore, from the viewpoint of suppressing the formation of heat transfer paths and achieving high heat insulation properties at high temperatures, it is desirable that the heat insulation layer has no binder.

(1) Organic additives Porous structures that have hydrophobic sites on the surface or inside are difficult to absorb water. Among these, silica airgel, hollow silica, and fumed silica cohesive structures have low specific gravity, so they easily float on water. For this reason, it is necessary to improve the water suspension of the porous structure to make it easier to disperse the porous structure when preparing a composition for a heat insulating layer using water as a solvent, and to improve the water dispersibility of the porous structure, and to adjust the From the viewpoint of adjusting the rheology and water retention of the composition for a heat insulating layer, it is desirable to incorporate an organic additive.

As the organic additive, for example, a surfactant may be used. The type of surfactant is not particularly limited, and can be appropriately selected from ionic surfactants (cationic surfactants, anionic surfactants, amphoteric surfactants) and nonionic surfactants. do it. One type of surfactant may be used alone, or two or more types may be used in combination. For example, when an ionic surfactant is used, even in a relatively small amount, it is possible to increase the viscosity of the composition for a heat insulating layer and to stabilize the dispersion of components such as porous structures in the composition for a heat insulating layer. Examples of the ionic surfactant include carboxymethyl cellulose sodium (CMC-Na), polycarboxylic acid amine salt, polycarboxylic acid ammonium salt, polycarboxylic acid sodium salt, TEMPO oxidized cellulose nanofiber (CNF-Na), and the like. When a nonionic surfactant is used, components such as a porous structure are more likely to be incorporated into a solvent when preparing a composition for a thermal insulation layer. In addition, when these components aggregate or separate in the heat insulating layer composition, they tend to be redispersed, and the solvent tends to be discharged when drying and forming the heat insulating layer. Examples of nonionic surfactants include polyethylene oxide (PEO) and polyvinyl alcohol (PVA). Further, it is preferable to use a nonionic surfactant and an ionic surfactant in combination because the effects of each of the above-mentioned surfactants can be adjusted as desired. For example, PEO's water retention is not very high. Therefore, when preparing the composition for a heat insulating layer, water is less likely to enter the gaps between the porous structures, and voids are less likely to occur when water evaporates during drying. As a result, the gaps between the porous structures are easily filled with infrared shielding particles. Moreover, the gaps between the large-diameter porous structures are easily filled with the small-diameter porous structures.

When blending organic additives, there is a risk that substances generated by decomposition or carbonization when exposed to high temperatures may form a heat transfer path and reduce the heat insulation properties. For example, one having a heating residue of 50% by mass or less at 600° C. is suitable because there are few products that deteriorate the heat insulation properties at high temperatures. Specific examples include PEO, CMC-Na, polycarboxylic acid amine salt, polycarboxylic acid ammonium salt, polycarboxylic acid sodium salt, TEMPO oxidized cellulose nanofiber (CNF-Na), PVA, and the like. The heating residue may be measured by thermogravimetric analysis (TGA). Specifically, approximately 5 mg of the organic additive was collected in a platinum pan, heated from room temperature to 600 °C at a temperature increase rate of 20 °C/min in a nitrogen gas atmosphere, and the mass before and after heating was calculated using the following formula ( Calculated by I).
Heating residue (%) = W ₁ /W ₀ ×100 ... (I)
[W ₀ : Sample mass before heating, W ₁ : Sample mass after heating]

If an organic additive is present on the surface or in the gaps of a component such as a porous structure, there is a risk that a heat transfer path will be formed through it. Therefore, from the viewpoint of suppressing the formation of heat transfer paths, the content of the organic additive should be 10% by mass or less, further 7% by mass or less, based on the total mass of the heat insulating layer as 100% by mass. It is desirable that there be.

(2) Reinforcing particles From the viewpoint of improving the mechanical strength of the heat insulating layer, reinforcing particles may be added to the heat insulating layer. The type of reinforcing particles is not particularly limited, and examples include relatively hard materials such as precipitated silica, gel silica, fused silica, wollastonite, potassium titanate, magnesium silicate, glass flakes, calcium carbonate, and barium sulfate; Inorganic particles with a large specific surface area can be used.

(3) Flame retardant Adding a flame retardant can impart flame retardancy to the heat insulating layer. As the flame retardant, known flame retardants such as halogen-based, phosphorus-based, metal hydroxide-based, etc. may be used. Considering the environmental impact, it is desirable to use phosphorus-based flame retardants. Examples of phosphorus-based flame retardants include ammonium polyphosphate, red phosphorus, and phosphate esters. Among these, those that are insoluble in water are desirable because the flame retardant is unlikely to flow out even if it comes into contact with moisture during use, and ammonium polyphosphate is preferred, for example.

<Base material>
The heat insulating material of the present disclosure only needs to include the heat insulating layer described above, and other configurations are not particularly limited. For example, it can be configured to include a base material that supports a heat insulating layer. In this case, the base material may be placed only on one side of the heat insulating layer in the thickness direction, or may be placed on both sides so as to sandwich the heat insulating layer. Alternatively, it may be a covering body in which the heat insulating layer is wrapped in a single base material. An adhesive layer may be interposed between the heat insulating layer and the base material. The adhesive layer may contain a flame retardant and the like in addition to the adhesive component.

Examples of the material of the base material include cloth, resin, paper, and steel plate. Examples of the fibers constituting the cloth include glass fibers, rock wool, ceramic fibers, alumina fibers, silica fibers, carbon fibers, metal fibers, polyimide fibers, aramid fibers, and polyphenylene sulfide (PPS) fibers. As ceramic fibers, refractory ceramic fibers (RCF), polycrystalline alumina fibers (PCW), and alkaline earth silicate (AES) fibers are known. Among them, AES fiber has higher safety because it has biosolubility. Examples of the resin include polyethylene terephthalate (PET), polyimide, polyamide, PPS, and the like. Examples of paper include pulp, a composite of pulp and magnesium silicate, and the like. Examples of the steel plate include galvalume steel plate (registered trademark), galvanized iron plate, stainless steel (SUS) plate, iron plate, titanium plate, and the like. The shape of the base material is not particularly limited, and examples include woven fabric, nonwoven fabric, film, and sheet. The base material may consist of a single layer or may be a laminate in which two or more layers of the same material or different materials are laminated.

For example, fabrics (woven fabrics) and non-woven fabrics made from inorganic fibers such as glass fibers and metal fibers, such as glass cloth, and fireproof insulation paper made as a composite material of pulp and magnesium silicate have comparatively high thermal conductivity. It has a small size and has high shape retention even in high-temperature environments. Furthermore, if a base material with high heat resistance is employed, the heat insulating material of the present disclosure can be used in applications that require high heat resistance, thereby expanding the applications of the heat insulating material of the present disclosure. Furthermore, safety is further improved by employing a base material having fire resistance. The base material with high heat resistance may be manufactured from glass fiber, rock wool, ceramic fiber, polyimide, PPS, etc. Specifically, glass fiber nonwoven fabric, glass cloth, aluminum glass cloth, AES wool paper, polyimide fiber nonwoven fabric, etc. Examples include.

<Method for manufacturing insulation material>
The heat insulating material of the present disclosure can be manufactured by pressure molding a material containing a porous structure, infrared shielding particles, inorganic fibers, and the like. Alternatively, it can be manufactured by applying a liquid (including slurry) composition for a heat insulating layer onto a base material and drying it. The coating may be applied using a brush, a coating machine such as a blade coater, a bar coater, a die coater, a comma coater (registered trademark), a roll coater, or a sprayer. Alternatively, the heat insulating layer composition may be manufactured by dipping the base material in the heat insulating layer composition or by forming the heat insulating layer composition on the base material by a papermaking method. Drying may be carried out at a temperature of 80 to 180° C. for several minutes to several tens of minutes.

The thickness of the heat insulating layer may be determined as appropriate depending on the application, and for example, from the viewpoint of heat insulation, it is desirable to set it to 0.1 mm or more, 0.5 mm or more, and even 1 mm or more. If the insulation layer is too thick, it not only increases cost, but also reduces strength and becomes brittle. For this reason, for example, 10 mm or less, 8 mm or less is suitable. In particular, from the viewpoint of reducing the thickness and increasing flexibility, it is desirable that the thickness be 5 mm or less, more preferably 3 mm or less.

Next, the present disclosure will be described in more detail with reference to Examples.

(1) Manufacture of heat insulating material samples A heat insulating material sample having the composition shown in Table 1 below was manufactured. First, silica airgel, infrared shielding particles, glass fibers, organic additives, and reinforcing particles were put into a kneader ("Trimix (registered trademark)" manufactured by Inoue Seisakusho Co., Ltd.) and stirred and mixed for 1 minute. While continuing to stir, water was added to make the solid content 40 to 50%, and for samples containing an inorganic binder (Comparative Examples 4 and 5 in Table 1 below), colloidal silica (water of silica particles) was added. A dispersion liquid ("LUDOX (registered trademark) LS" manufactured by Sigma-Aldrich) was added. Then, stirring and mixing were further performed for 15 minutes. After that, stirring was continued for an additional 30 minutes while stopping the stirring every 2 minutes and scraping off the material adhering to the inner wall of the container, the blade surface, etc. with a spatula, and the mixture was mixed for an additional 30 minutes. was manufactured.

Details of the materials used are as follows.
Silica airgel powder: "Aerogel Particles P200" manufactured by Cabot Corporation, particle size 0.1 mm to 1.2 mm.
Glass fiber: "Wet Chop" manufactured by Nippon Electric Glass Co., Ltd., length 3 mm, filament diameter 6.5 μm.
Silicon carbide (SiC) powder: "Fuji Random GC" manufactured by Fuji Seisakusho Co., Ltd., particle size standard #4000.
Titanium oxide (TiO ₂ ) powder: “High purity titanium oxide HT0110” manufactured by Toho Titanium Co., Ltd.
PEO: Polyethylene oxide manufactured by Sigma-Aldrich, viscosity average molecular weight ~1 million.
CMC: Carboxylmethylcellulose sodium salt manufactured by Sigma-Aldrich, molecular weight 380,000.
Wet silica: "Nipsil (registered trademark) NS-K" manufactured by Tosoh Silica Co., Ltd.

Next, a pedestal was prepared in which a first spacer plate made of SUS was placed on top of glass fiber paper. The thickness of the first spacer plate is 4 mm, and a 150 mm square injection hole is formed in the center. The produced composition for a heat insulating layer was filled into the injection hole of the first spacer plate and formed into a plate shape. After that, the first spacer plate is removed, another second spacer plate is placed, and glass fiber paper is layered on top of it. A laminate was manufactured. The thickness of the second spacer plate is 3 mm, and like the first spacer plate, a square injection hole of 150 mm square is formed in the center. A heat insulating layer composition is placed in the injection hole of the second spacer plate. Separately, a first plate material made of aluminum and having a thickness of 5 mm and a square size of 320 mm, and a second plate material made of aluminum and having a thickness of 1 mm and a square size of 320 mm were prepared. A plurality of grooves are formed on one surface of the first plate. The plurality of grooves each have a linear shape of 2.5 mm in width, 3 mm in depth, and 200 mm in length, and are formed in parallel at 5 mm intervals. Punching holes with a diameter of 1 mm are formed throughout the second plate material at intervals of 2 mm. The second plate material was stacked on one side of the first plate material, and the laminate was placed on top of the second plate material. Then, the second plate material was placed on top of the laminate, and the first plate material was further stacked so that one side on which the groove was formed was on the second plate material side. In this state, pressure drying using a hot press was performed for 30 minutes at a temperature of 165° C. and a load of about 98 kN. Thereafter, it was allowed to cool to room temperature, and the first plate material, second plate material, upper and lower glass fiber papers, and second spacer plate were removed to obtain a plate-shaped heat insulating material sample with a thickness of 3 mm.

Among the obtained insulation material samples, the reference number of silica airgel was measured for the samples of Examples 1 and 3 in Table 1 below. The measurement method is as follows. First, a test piece of a predetermined size was cut out from a heat insulating material sample and coated with platinum as a pretreatment. Thereafter, cross section processing was performed using a "Cross Section Polisher (registered trademark) SM09010" manufactured by JEOL Ltd. at an acceleration voltage of 4 kV and a processing time of 20 hours. Next, the cross section after processing was treated with an osmium coat to make it conductive, and a backscattered electron image and a cross-sectional photograph were taken using a "SEM S-3400N" manufactured by Hitachi, Ltd. at an acceleration voltage of 15 kV and a magnification of 200 times. Five straight lines each having a length of 400 μm were drawn in parallel at 40 μm intervals on the obtained cross-sectional photograph, and the number of silica airgel that intersected each straight line was counted. Then, the number of silica airgel was totaled, and the value was divided by 5 to obtain a reference number. As a result, the reference number of samples of Example 1 was 26.4, and the reference number of samples of Example 3 was 16.2.

(2) Measurement of thermal conductivity The thermal conductivity of the manufactured insulation material sample was measured using the “Quick Thermal Conductivity Meter QTM-700” and “High Temperature Probe PD-31N” manufactured by Kyoto Electronics Co., Ltd. , was measured as follows. First, the upper and lower sides of the probe were sandwiched between two heat insulation samples stacked one on top of the other, and a weight was placed on top of the probe to prevent it from being crushed, and the probe was placed in an electric furnace. Then, the temperature inside the electric furnace was raised to 800° C., and after the temperature inside the furnace was stabilized, the thermal conductivity was measured.

(3) Evaluation of heat insulation properties Table 1 shows the composition of the heat insulating material sample and the evaluation results of heat insulation properties based on the measurement results of thermal conductivity. The thermal insulation evaluation is passed if the thermal conductivity is less than 0.3 W/m・K (indicated by a circle in the table), and rejected if the thermal conductivity is 0.3 W/m・K or more ( (indicated by an x in the table).

As shown in Table 1, the samples of Examples 1 to 7 that satisfy the conditions (a) to (d) above all have a thermal conductivity of less than 0.3 W/m・K, and can be used at high temperatures. It was also confirmed that it has excellent heat insulation properties. In contrast, the sample of Comparative Example 1 does not contain infrared shielding particles and does not satisfy conditions (b) to (d). The sample of Comparative Example 2 has a ratio of silica airgel content to infrared shielding particle content of 0.5, and does not satisfy condition (d). The sample of Comparative Example 3 has an infrared shielding particle content of 0.5% by mass, and does not satisfy condition (b). The sample of Comparative Example 4 does not contain infrared shielding particles and does not satisfy conditions (b) to (d). The sample of Comparative Example 5 has a total content of silica airgel and infrared shielding particles of 50% by mass, and does not satisfy condition (c). Therefore, the samples of Comparative Examples 1 to 5 all had a thermal conductivity of 0.3 W/m·K or more, and it was not possible to obtain the desired heat insulation properties at high temperatures.

The heat insulating material of the present disclosure is suitable for use as a heat insulating material for vehicles, a heat insulating material for houses, a heat insulating material for electronic devices, a heat insulating material for heat/cold containers, and the like. Among these, it is suitable for use in battery packs, heat-not-burn cigarettes, heat-insulating sheets for fire prevention, etc., which require insulation properties in high-temperature atmospheres.

10: Heat insulation layer (cross-sectional photo), 11: Porous structure, 12: Infrared shielding particles, 13: Inorganic fiber.

Claims

A porous structure in which a plurality of particles are connected to form a skeleton, have pores inside, and have a hydrophobic site at least on the surface and inside, infrared shielding particles, and inorganic fibers, A heat insulating material characterized by comprising a heat insulating layer that satisfies the following conditions (a) to (d).
(a) The content of the inorganic fiber is 5% by mass or more and 25% by mass or less.
(b) The content of the infrared shielding particles is 10% by mass or more.
(c) The combined content of the porous structure and the infrared shielding particles is 70% by mass or more.
(d) The ratio of the content of the porous structure to the content of the infrared shielding particles is 1.2 or more.
The content of each component under the conditions (a) to (d) is calculated based on the total mass of the heat insulating layer as 100% by mass.
The heat insulating material according to claim 1, wherein the reference number calculated by the following steps (i) to (iii) as an index indicating the filling state of the porous structure in the heat insulating layer is 10 or more.
(i) A cross section in the thickness direction of the heat insulating layer is photographed using a scanning electron microscope at a magnification of 200 times, and five straight lines each having a length of 400 μm are drawn in parallel at 40 μm intervals on the obtained cross-sectional photograph.
(ii) For each straight line drawn, count the number of porous structures that intersect with the straight line, and calculate the total.
(iii) Divide the calculated total by 5 to obtain the reference number of porous structures.
The heat insulating material according to claim 1 or 2, wherein the average particle diameter of the infrared shielding particles is 0.3 μm or more and 22 μm or less.
The heat insulating material according to any one of claims 1 to 3, wherein the infrared shielding particles include high emissivity particles having an emissivity of 0.6 or more in the infrared wavelength region.
The heat insulating material according to any one of claims 1 to 4, wherein the infrared shielding particles include high refractive index particles having a refractive index of 2.0 or more in the wavelength region of visible light.
The heat insulating material according to any one of claims 1 to 5, wherein the heat insulating layer further contains an organic additive.
The heat insulating material according to claim 6, wherein the organic additive includes a surfactant.
The heat insulating material according to claim 7, wherein the surfactant includes a nonionic surfactant.
The heat insulating material according to claim 7, wherein the surfactant includes both a nonionic surfactant and an ionic surfactant.
The heat insulating material according to any one of claims 6 to 9, wherein the organic additive has a heating residue of 50% by mass or less at 600°C.
The heat insulating material according to any one of claims 1 to 10, wherein the length of the inorganic fiber is 16 mm or less.
The heat insulating material according to any one of claims 1 to 11, wherein the porous structure includes silica airgel in which a plurality of fine silica particles are connected to form a skeleton.
The heat insulating material according to any one of claims 1 to 12, wherein the porous structure has a cohesive structure in which a plurality of fumed silica fine particles are connected to form a skeleton.
The heat insulating material according to any one of claims 1 to 13, wherein the heat insulating layer does not include a binder.
The heat insulating material according to any one of claims 1 to 14, further comprising a base material laminated on the heat insulating layer.
The heat insulating material according to any one of claims 1 to 15, wherein the infrared shielding particles include silicon carbide particles.
The heat insulating material according to any one of claims 1 to 16, wherein the infrared shielding particles include titanium oxide particles.